stroker=high compression...low hp?

[moonraker]

hey guys sorry for the newbish title but i have a 1g engine in 95' gst with FMIC, 880cc injectors, walbro 255lph, dsm chip, 3" turboback exhaust, went from a 20g to a DBB 5031 50 trim turbo. got eagle rods, arp studs, eliminated the balance shafts, and got a lightened fidanza flywheel. i stroked it to 2.3l and notice the compression ranging from 195-205, which seems very high.. I have the wiseco 8.8:1 stroker pistons in there. when tuning i have to bring down timing below stock when turbo kicks in because of knock. i havnt dynod it officially yet, but i use streetdyno just to get an idea of where im at. it records 308hp and 331 lbs torque on 20 lbs of boost... what i want to know is did i screw myself with the 8.8:1 pistons? can i double the headgasket to lower compression? when i had the 20g, no stroked and 550 injectors i believe i was running 311hp on low boost like 15psi. i forgot to mention im on stock cams but i cant imagine they would reduce hp that much?

any help would be appreciated thnx.

 

[slipstream808]

No, in fact people often choose 9:1 or 9.5:1 compressions pistons on their 2.3's.

You are dropping your timing due to the aggressive 1g timing curve. Since they came stock with 7.8:1 CR pistons, they needed it. With 8.8:1's, you don't need that kind of timing.

 

[andymoraitis]

No, in fact people often choose 9:1 or 9.5:1 compressions pistons on their 2.3's.

You are dropping your timing due to the aggressive 1g timing curve. Since they came stock with 7.8:1 CR pistons, they needed it. With 8.8:1's, you don't need that kind of timing.

That's exactly right. Even the stock 2G timing curve which peaks at 16 degrees above 2.1 g/rev may be too much if you can't maintain cool enough intake air temps. I was able to run mine at a max of 12 degrees of timing on pump at 25 psi with the 8.8:1 compression ratio and Comp 200's straight up. Advancing the intake cam a bunch necessitated even more of a timing drop since cylinder compression went from 170 across to almost 190 across. I now run a peak of 8 degrees at the same boost pressure on a minimal knock tune and on average I see maybe 1-2 counts after the intercooler has heatsoaked.

You have forged internals so it can handle the low timing. I really wouldn't go below 8, but you can try 10-12 and see what that nets you. On pump gas, it'll always be boost over timing to make strong power. 25 psi at 8 degrees will make more than 20 psi at 12 degrees. Don't get me wrong. Strokers really do like timing, but if you're unable to run a certain amount due to knock constraints, then pulling the timing and upping the boost is a very viable compromise. With respect to your tuning, if the Keydiver chip is your only tuning aid and it's on stock timing and A/F maps, there's a ton of power on the table. While I use a Keydiver as well, mine is set up with a custom A/F on the four highest load maps (11.5:1) and has peak timing set to 8 degrees with a bit more timing in the midrange to get the car moving. Stock maps run at a pig rich 9.5:1 A/F and timing is based on whether it's a first or second gen motor.

I didn't notice aftermarket cams in your mod list so that would certainly explain why your compression numbers are so high. Cams make a huge difference in how a stroker performs. Consider that you have a bottom end with the capacity to move much more air than an equivalent 2.0 and you'll see how the stock cams are a restriction. I'd recommend any of the more common combinations with a set of adjustable cam gears to dial them in properly. Please keep us posted as to your results since there's a lot of power left in your combo. Also, please fill out your mod list in your profile so we can help you more easily in the future.

Hope that makes sense,

Andy

 

[moonraker]

thanks for the info that helps alot. so the next step would be to get some aftermarket cams. i had web cams with the 20g setup, but vaccum was pretty bad and made for nasty idle. do you think HKS 272 cams with the adjustable gears would be the best for the setup? with the current setup now with stock cams i have a rough idle that will sometimes turn off the car if i press the clutch while the rpms are 2k and up. but if i go with aftermarket cams i wanna go with the best , so would HKS 272s be good for my setup?

 

[andymoraitis]

I think the cams are what's holding you back from making more power, but the timing issue needs to be addressed right away if you want to see strong boost on pump gas. Dial your max timing down to 8 degrees and see what that nets you for knock.

For cams, it's really not that big a deal which ones you choose. My Comp 200's used to idle like stock until we advanced the intake cam. Now it sounds like a big block Mustang. At 1000 RPM, I pull about 9 inches of vacuum and around 21 on a hard decel. The cam advance definitely gives the motor more snap.

I think you'd be fine with 272's, FP2's, Webs or Comp 200's. A lot of people really like the new Brian Crower cams as well as the DKS cams from FFWD Connection. Cam gears will definitely help you dial them in and I'll be investing in a set soon as well.

Oh and don't forget to fill out your profile.

Keep us posted and I'm glad the info helped.

Andy

 

[moonraker]

i have heard there are crower cams made for the stroker engine, they are 282s i believe. do you think this would be a good buy for my setup? i dont want to have to change cams later on. im looking into water injection after i get the cams.

 

[moonraker]

actually im sorry i just went onto the crower website and saw the stage 3 which are 280's and the stage 4's which are 288's. do you think the stage 4's are streetable?